Did a 'lost star' knock Earth off its orbit?

WASHINGTON: Ever wondered why the Earth's orbit is tilted to the Sun's equator?

A new theory suggests an errant young star strayed close and pulled our developing planet out of whack with the Sun's equator. Accounting for planets that circle their stars on tilted paths, this idea may also explains why Earth's orbit is tipped 7 relative to the Sun's equator, the 'ScienceNOW' reported.

Konstantin Batygin of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts, suggests that Sun had a near stellar neighbour at the time Earth was formed.

In 1995, Swiss astronomers made the shocking discovery of the first "hot Jupiter," a gas giant circling close to its star.

"Misaligned orbits are actually a natural outcome of disk migration - once you take into account the fact that planetary systems are usually born in multistellar environments," Batygin said.

In work appearing in journal Nature, Batygin calculates how a young star's protoplanetary disk gets torqued by a second star orbiting the first. When a giant planet spirals inward through this tilted disk, it ends up on a path that's out of whack with its sun's equator. "I think it's an entirely plausible idea," says astronomer Josh Winn.

"The best thing about it is we can test it," he said. If Batygin is right, Winn says, then misalignments should be just as common in solar systems that lack hot Jupiters, because tilting a disk doesn't require their presence.

Nasa's Kepler spacecraft has measured the tilt of just one multiplanet system: the three planets around Kepler 30, all of which have orbits that line up with their star's equator. "I think somewhere in the Milky Way, there's a star that's responsible for tilting us," Batygin says. He suspects the Sun once had a companion star that tipped the solar nebula by 7 degree, then fled the scene after planets arose. pti